But apparently they had very little difficulty obtaining guns. Not exactly an argument against stricter gun control.

Finding out how they got the guns could be illustrative. If they bought them at a gun show they'd be in the very small minority of criminals who do so... and Massachusetts may be a state that requires background checks at gun shows (many in New England do, I'd be surprised if Mass. didn't in fact). But it's all conjecture until we have some idea how they got the guns, if we ever find out. The younger one was 19, so him obtaining a handgun legally was impossible (need to be 21 to obtain a handgun, you can't even shoot a handgun at an indoor range in Michigan under 21, I've seen people turned away for that very reason.)